Answer: Abiotic factor for polar: Ice
Abiotic for desert: Sand
Biotic for polar: Polar bears
Biotic for desert: Cacti
The types of factors are different because there are different set conditions for each ecosystem. A cactus is built for it's hot, dry ecosystem. If it were to move to a polar ecosystem it would not survive there. Same for the polar bear. It's built for polar regions. It has white fur to blend with the white ice to help it blend in and it's adapted to swim to get it's food source.
Explanation:
 
        
                    
             
        
        
        
Answer:
DNA replication needs to occur because existing cells divide to produce new cells. Each cell needs a full instruction manual to operate properly. So the DNA needs to be copied before cell division so that each new cell receives a full set of instructions!
 
        
             
        
        
        
Answer:
All of these are correct
Explanation:
According to the question, marble is a rock formed from limestone, which in turn is also formed from Calcite. This shows that marble is a kind of metamorphic rock because a metamorphic rock is any rock that is formed by the alteration of other rocks caused by heat, pressure or chemicals etc. These changes that occurs in the previously existing rocks are called METAMORPHOSIS. 
Hence, since marble is formed from limestone, it concludes that marble is a metamorphosed rock formed from a previously existing limestone rock. Also, since Calcite, a precursor of limestone that marble is formed from can be degraded by acids, both limestone and marble which are formed from it will also be dissolvable by acids. 
 
        
             
        
        
        
Answer:
For question 20. I believe the answer is C. There would be more iguanas with webbed feet.
Explanation:
It states the iguanas have adapted to different habitats on the island. The iguanas that have webbed feet will be better at getting food in water, but slower on land. So if the land starts to disappear and turns into more water, the iguanas with webbed feet will have a higher chance of survival. Meaning the iguanas with out webbed feet will die out as a population.